JP2000128654A - Silicon nitride composite substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a Si3N4 composite substrate not causing cracks in the substrate even by mechanical impacts and thermal impacts an having excellent heat-releasing characteristics and heat cycle-resistant characteristics by using a Si3N4 substrate as a ceramic substrate. SOLUTION: This Si3N4 composite substrate is obtained by using a Si3N4 substrate having a heat conductivity of >=90 W/m.K and a three point bending strength of >=700 MPa and setting a metal layer tm joined to the main surface of one side of the Si3N4 substrate and the thickness tc of the Si3N4 substrate so as to satisfy a relation: 2 tm <=tc<=20 tm. When metal layers are joined to the main surfaces of both the sides of the Si3N4 substrate, the total thickness ttm of the metal layers on both the main surfaces satisfies a relation: ttm<=tc<=10 ttm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a composite substrate such as a power module on which a heat-generating electronic component such as a semiconductor element is mounted, and more particularly to a structure in which a metal layer is bonded to a ceramic substrate, heat radiation characteristics, and mechanical strength. And a ceramic composite substrate having excellent heat cycle characteristics.

[0002]

_2. Description of the Related Art Conventionally, as a component of various electronic devices, a metal plate mainly composed of copper or aluminum as a conductive layer is formed on a surface of a ceramic substrate made of Al ₂ O ₃ , AlN, BeO or the like having electrical insulation. Have been widely used.

Among these conventional ceramic composite substrates, those using an Al ₂ O ₃ substrate as the ceramic substrate cannot provide good heat radiation because of the low thermal conductivity of Al ₂ O ₃ , and cannot be used for a BeO substrate. Although the use of is high in heat conductivity and excellent in heat dissipation, there is a problem that it is difficult to handle in production due to its toxicity. In addition, a composite substrate using an AlN substrate is excellent in heat dissipation because of the high thermal conductivity of AlN. However, since the mechanical strength of AlN is low, it can be used in mechanical shock or when repeatedly used under actual use. The thermal load of
There was a problem that cracks were easily formed.

On the other hand, ceramics containing Si ₃ N ₄ as a main component generally exhibit excellent heat resistance even in a high temperature environment of 1000 ° C. or more, and have a low thermal expansion coefficient, in addition to the inherent high strength characteristics. Since it is a material having excellent impact resistance, application to various high-temperature and high-strength components as a high-temperature structural material has been attempted.

[0005]

Recently, the use as a ceramic substrate for a composite substrate has been studied by utilizing the inherent high strength characteristics of ceramics containing Si ₃ N ₄ as a main component. For example, JP-A-269870 and JP-A-9-157054 disclose a composite circuit board in which a metal circuit board is bonded to a Si ₃ N ₄ board, and the Si ₃ N ₄
There is disclosed an attempt to compensate for insufficient thermal conductivity by making the thickness of the substrate smaller than 1 mm, and to enhance the heat dissipation of the entire circuit.

However, Si ₃ N ₄ , which has higher strength than AlN,
However, if the thickness of the substrate is small,
Like the N-substrate, cracks are likely to occur due to mechanical shock at the time of mounting and mounting, and thermal shock due to thermal cycling, and it is considered that practical application is difficult. For example, in the process of assembling a ceramic composite substrate into a device, it is necessary to fix the composite substrate to the main part of the device by screwing or the like. Even if the substrate is a Si ₃ N ₄ substrate having excellent mechanical strength, the substrate is thin. This is because the generation of cracks due to the pressing force of the screws and the impact during handling is inevitable. When such a crack occurs, insulation failure occurs at the crack, and the composite substrate becomes unusable due to insulation breakdown.

The present invention has been made in view of such a conventional situation,
It is an object of the present invention to provide a ceramic composite substrate in which a ceramic substrate is not cracked even by a mechanical shock or a thermal shock, and is excellent in heat radiation characteristics and heat resistance cycle characteristics.

[0008]

In order to achieve the above object, the present inventors have developed a high thermal conductivity and high strength Si ₃ N _4.
In addition to researching and developing substrate materials, when the thickness of the Si ₃ N ₄ substrate and the thickness of the metal plate are set to a predetermined ratio to form a composite substrate, tightening cracks and the like during the assembly process are eliminated, greatly improving the heat cycle characteristics. The present invention has been found that the heat dissipation of the composite substrate can be greatly improved by increasing the thermal conductivity of the Si ₃ N ₄ substrate.

That is, a ceramic composite substrate provided by the present invention includes a silicon nitride ceramic substrate having a thermal conductivity of 90 W / m · K or more and a three-point bending strength of 700 MPa or more;
A metal layer bonded on one of the main surfaces, the thickness of the silicon nitride ceramic substrate is tc, and the thickness of the metal layer is tm.
Where tc and tm are the relational expression 2tm ≦ tc ≦ 20t
m.

Another silicon nitride composite substrate provided by the present invention includes a silicon nitride ceramic substrate having a thermal conductivity of 90 W / m · K or more and a three-point bending strength of 700 MPa or more, and a silicon nitride ceramic substrate on both main surfaces thereof. When the thickness of the silicon nitride ceramic substrate is tc and the total thickness of the metal layers on both main surfaces is ttm, tc and ttm satisfy the relational expression ttm ≦ tc ≦ 10ttm. It is characterized by the following.

In the silicon nitride composite substrate of the present invention,
It is preferable that the silicon nitride ceramic substrate before metal plate bonding has a warp such that the main surface on the side on which the semiconductor element is mounted is concave, and the specific amount of warp is a substrate length of 25.4 mm.
It is preferably within the range of 10 to 300 μm per (inch).

The silicon nitride ceramic substrate used for the silicon nitride composite substrate of the present invention has a rare earth element content of 0.6 to 10% by weight in terms of oxide and at least one selected from Mg, Ti, Ta, Li and Ca. Contains 0.5% to 1.0% by weight of one element in oxide, 2% by weight or less of oxygen as impurities, and 0.2% by weight or less of Al in oxide It is characterized by.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, a Si ₃ N ₄ substrate used for a ceramic composite substrate of the present invention will be described below. The ceramic substrate used for the composite substrate needs to be a dense sintered body having both high thermal conductivity and high strength characteristics. The low thermal conductivity of the conventional Si ₃ N ₄ sintered body is due to the Si
_This is because impurities are dissolved in ₃ N ₄ grains and phonons, which are carriers of heat conduction, are scattered. Since Si ₃ N ₄ is a hard-to-sinter ceramic, it is necessary to add a sintering aid that generates a liquid phase at a low temperature. It is known to reduce

Therefore, in the present invention, the type of the sintering aid is selected, and the amount of the sintering additive is set within a predetermined range, thereby providing not only the original excellent mechanical strength but also the Si ₃ N ₄ sintered body. To improve and improve the thermal conductivity of the ceramic substrate. That is, in the present invention, as a sintering aid for Si ₃ N ₄ , rare earth oxides, Mg, Ti, Ta, Li, C
At least one oxide of a is used in combination.

Since rare earth oxides hardly form a solid solution in Si ₃ N ₄ grains, they are effective for increasing the thermal conductivity of the sintered body. Among rare earth oxides, it is desirable to use oxides of Y, Yb, and Sm. This is because when these oxides are used, the grain boundary phase is easily crystallized. When the grain boundary phase is crystallized, the high-temperature strength is increased, and at the same time, the scattering of phonons in the grain boundary phase is reduced, which is effective for simultaneously achieving high strength and high thermal conductivity. Further, the amount of these rare earth oxides added is 0.1.
A range of 6 to 10% by weight is preferred. If the amount is less than 0.6% by weight, a liquid phase is not sufficiently generated, and the densification does not proceed in the sintering process, so that the porosity after sintering increases and the thermal conductivity decreases. The mechanical strength is also low. On the other hand, when the content is more than 10% by weight, the ratio of the grain boundary phase in the sintered body increases, and the thermal conductivity decreases.

Other sintering aids such as Mg, Ti, Ta, L
The oxides of i and Ca are Si ₃ N ₄ at a temperature of 1600 ° C. or less.
It is effective for generating a liquid phase by reacting with SiO ₂ on the particle surface and promoting densification in the sintering process. These oxides greatly improve the sinterability and reduce the thermal conductivity by adding a small amount of 0.5 to 1% by weight in total, as compared with the case where the rare earth oxide is added alone. Has little effect. However, if the total added amount of these oxides of Mg, Ti, Ta, and Ca exceeds 1% by weight, these elements may form a solid solution in the Si ₃ N ₄ grains, and the thermal conductivity may be significantly reduced. is there. Further, when Mg, Ti, Ta, Li, and Ca are included in the grain boundary phase component, a non-crystalline glass component is formed in the grain boundary phase, so that the thermal conductivity also decreases, and the strength at high temperatures also decreases. descend.

Further, by increasing the purity of the raw material powder, the thermal conductivity of the obtained Si ₃ N ₄ sintered body can be improved. It is widely known that oxygen and Al easily dissolve in Si ₃ N ₄ grains to lower the thermal conductivity. Therefore, in the Si ₃ N ₄ substrate of the present invention, the oxygen content is set to 2% by weight or less and Al is set to 0.2% by weight or less as impurities in the raw material powder of the sintered body, particularly in the Si ₃ N ₄ powder. Thereby, the thermal conductivity of the Si ₃ N ₄ sintered body can be further improved.

The thus produced Si ₃ N ₄ sintered body has a thermal conductivity at room temperature of 90 W / m · K or more, and
It has excellent properties with a point bending strength of 700 MPa or more. Thus, by increasing the thermal conductivity further than the conventional high thermal conductivity Si ₃ N ₄ substrate and at the same time increasing the mechanical strength, the thermal resistance of the entire ceramic composite substrate is reduced, and the thickness of the ceramic substrate is reduced. Can be increased to a thickness that can withstand thermal and mechanical shocks.

That is, in the silicon nitride composite substrate of the present invention, a Si ₃ N ₄ substrate having a thermal conductivity of 90 W / m · K or more and a three-point bending strength of 700 MPa or more is used. When joining the layers, when the thickness of the Si ₃ N ₄ substrate is tc and the thickness of the metal layer is tm, this tc
And the thickness of the ceramic substrate is set so that tm satisfies the relational expression 1 of 2 tm ≦ tc ≦ 20 tm.

In order to improve the heat-resistant cycle characteristics of the ceramic composite substrate, it is effective to bond a metal layer to both main surfaces of the ceramic substrate. Assuming that the total thickness of the layers is ttm, tc and ttm satisfy ttm ≦ tc ≦ 10ttm.
The thickness of the ceramic substrate is set so as to satisfy the relational expression 2. At this time, it is preferable to satisfy the above relational expression 1 at the same time. Further, the thickness of the metal layer bonded to both main surfaces may be the same or different.

In the above relationship between tc and tm or ttm, when the metal layer is on one of the main surfaces of the Si ₃ N ₄ substrate, S
If the thickness tc of the i ₃ N ₄ substrate is tc <2 tm, or if it is tc <ttm when both are on the main surface, mounting is possible even with the high-strength Si ₃ N ₄ substrate as described above. Cracks are likely to occur due to mechanical shock at the time, and cracks are likely to occur due to thermal cycling. When the metal layer is on one side of the main surface, tc
> 20 tm or tc> t when both are on the main surface
If tm, the thermal resistance of the entire composite substrate increases, which is not preferable.

The specific thickness of the Si ₃ N ₄ substrate is 1 mm in order to prevent cracks and breakage due to mechanical impact.
It is preferable to make the above. However, if the Si ₃ N ₄ substrate is too thick, the heat radiation characteristics and the heat cycle characteristics as a whole deteriorate, so that it is preferable that the thickness be approximately 6 mm or less.

It is preferable that the Si ₃ N ₄ substrate of the present invention has a warp in which the main surface on the side on which the semiconductor element is mounted becomes concave at an initial stage before joining the metal layers. Further, it is preferable that the amount of the warpage is in the range of 10 to 300 μm per 25.4 mm (1 inch) of the length of the main surface of the Si ₃ N ₄ substrate.

When a metal plate is bonded to a concave main surface of a Si ₃ N ₄ substrate having such a warp and a device such as a transistor chip as a heat source is mounted thereon, the amount of heat generated by the device is reduced. When the temperature of the entire circuit rises due to the increase, the heat causes a tensile stress to act on the principal surface on the element mounting side of the Si ₃ N ₄ substrate and a compressive stress to act on the principal surface on the opposite side. As a result, the Si ₃ N ₄ substrate, which was initially warped concavely toward the element mounting side, is deformed in a direction parallel to the main part of the device, and the adhesion between the device and the substrate is improved. Resistance can be further reduced.

[0025]

EXAMPLE 1 An Si ₃ N ₄ powder having an oxygen content of 1% by weight and an average particle diameter of 0.9 μm was mixed with a Y ₂ O ₃ powder of 8% by weight of the Si ₃ N ₄ powder (an average particle diameter of 1.0 μm). ) And 0.5% by weight of MgO powder (average particle size: 1.0 μm) were mixed in an alcohol solvent by a ball mill. Thereafter, the mixture of the raw material powders was dried, a binder component was added and kneaded, and a plurality of sheet-like molded bodies were produced by a dry mold press. After the molded body was degreased in a nitrogen atmosphere, it was baked at 1800 ° C. for 4 hours in a nitrogen atmosphere to obtain a Si ₃ N ₄ sintered body. The impurity Al in the sintered body
As a result of quantification of the amount by ICP emission spectrometry, it was about 0.1% by weight. This impurity Al is considered to be derived from the raw material.

Next, a sample for measuring heat conduction having a diameter of 10 mm and a thickness of 3 mm was processed from a part of each of the obtained Si ₃ N ₄ sintered bodies, and the thermal diffusivity was measured by a laser flash method. Equation K = α × C × ρ (α: thermal diffusivity, C: specific heat,
(ρ: density) to calculate the thermal conductivity. In addition, each Si ₃
Some N ₄ sintered body, 4 × 3 × 40m by grinding
A bending test piece of m was prepared and subjected to a three-point bending test of JIS standard (R-1601) with a span of 30 mm. as a result,
The thermal conductivity of this Si ₃ N ₄ sintered body was 110 W / m · K, and the three-point bending strength was 950 MPa.

The obtained Si ₃ N ₄ sintered body was machined by grinding and polishing with a length and width of 32 × 75 mm and the thickness was changed as shown in Table 1 below to obtain Si ₃ N ₄ substrates. . The amount of warpage per 25.4 mm (1 inch) length of each substrate was measured, and the results are shown in Table 1. Sample 1
6, the thickness tm or the total thickness ttm shown in Table 1 is provided on the concave main surface, and on the main surfaces on both sides in Samples 7 to 10, respectively.
Oxygen-free copper plate is joined using a brazing material containing active metal,
A ceramic composite substrate was obtained.

After joining the Si ₃ N ₄ substrate and the copper plate, it was confirmed by ultrasonic testing that there was no gap between the substrate and the copper plate, and then each composite substrate was subjected to a heat cycle test. In the heat cycle test, the composite substrate was cooled at −40 ° C. for 20 minutes, kept at room temperature for 20 minutes, heated at 125 ° C. for 20 minutes, and further kept at room temperature for 20 minutes as one cycle. The presence or absence of crack generation and the number of heat cycles until crack generation were confirmed. Further, the thermal resistance of each composite substrate was measured, and the heat radiation characteristics of the entire circuit were examined. The measurement of the thermal resistance was performed by placing one piece on the copper plate bonded to the concave main surface of the composite substrate.
The evaluation was performed by mounting a 0 × 10 mm Si transistor chip as a heat source. These results are shown in Table 1 below.

[0029]

[Table 1] Substrate thickness Copper plate thickness tc / tm Warpage amount Thermal resistance sample when cracks occur tc (mm) tm, ttm (mm) (tc / ttm) (μm / in) Number of cracks Number of heat cycles (° C / W ) 1 2 0.3 6.7 100 0> 3000 0.6 2 1 0.3 3.3 200 0> 3000 0.3 3 0.6 0.3 2.0 250 0> 3000 0.25 4 5 0.3 16.7 15 0> 3000 1.25 * 6.3 0.3 21.0 9 0> 3000 2.0 6 * 0.5 0.3 1.67 310 4 1500 0.3 7 2 0.3 + 0.3 3.3 95 0> 3000 0.4 8 5 0.3 + 0.3 8.3 10 0> 3000 0.89 2 0.1 + 0.3 5.0 90 0> 3000 0.5 10 2 1.5 + 0.3 1.1 90 0> 3000 0.3 (Note) Samples marked with * in the table are comparative examples. In addition, the total thickness ttm of the copper plates of Samples 7 to 10 was represented by the sum of the thickness of each main surface.

As can be seen from the results, the thermal conductivity is 1
Si _{3 with} 10 W / m · K and three-point bending strength of 950 MPa
Using an N ₄ substrate, the thickness tc of the substrate and the thickness tm of the metal layer or the total thickness ttm are set to 2 ≦ tc / tm ≦ 20 or 1 ≦ tc.
In each sample of the present invention adjusted so as to satisfy / ttm ≦ 10, no crack was generated in the Si ₃ N ₄ substrate even when the number of cycles reached 3,000 in the heat cycle test, and at the same time, the thermal resistance of the entire composite substrate was reduced. The values were also small, demonstrating that excellent heat dissipation characteristics were exhibited.

On the other hand, tc / tm> 20 or tc / ttm
In the composite substrate of Sample 5 of Comparative Example in which> 10, Si ₃ N ₄
Since the thickness of the substrate was too large, the heat radiation characteristics of the entire circuit were inferior, and the thermal resistance of the entire composite substrate was extremely high at 2.0 ° C./W. Also, tc / tm <2 or tc / ttm <1
In the sample 6 of the comparative example, the heat-resistant cycle characteristics were deteriorated by reducing the thickness of the Si ₃ N ₄ substrate, and cracks were generated in the heat cycle test while the number of cycles was small.
In samples 3 and 6 in which the thickness of the Si ₃ N ₄ substrate was less than 1 mm, cracks and breaks were likely to occur on the substrate due to mechanical impact in the assembly process.

Example 2 A Si ₃ N ₄ substrate was prepared in the same manner as in Example 1 except that the type and amount of the sintering aid added to the Si ₃ N ₄ powder were changed as shown in Table 2 below. It was fabricated and its thermal conductivity and three-point bending strength were similarly evaluated. These results are also shown in Table 2. Table 2 also shows the Si ₃ N ₄ substrate of Example 1 (sample 1) for reference. In addition, each Si ₃ N ₄
As in the samples of Example 1, the amount of impurities in the substrate was 1% by weight of oxygen and 0.1% by weight of Al.

[0033]

[Table 2] Thermal conductivity 3-point bending strength sample Type and amount of sintering aid (wt%) (W / m · K) (MPa) 1 Y ₂ O ₃ (8) + MgO (0.5) 110 950 11 Sm ₂ O ₃ (8) + MgO (0.5) 110 900 12 Yb ₂ O ₃ (8) + MgO (0.5) 140 900 13 Y ₂ O ₃ (4) + Yb ₂ O ₃ (4) + MgO (0.5) 138 900 14 Y ₂ O ₃ (4) + Sm ₂ O ₃ (4) + MgO (0.5) 100 1000 15 Yb ₂ O ₃ (4) + Sm ₂ O ₃ (4) + MgO (0.5) 105 950 16 Y ₂ O ₃ (8) + TiO ₂ (0.5) 110 900 17 Y ₂ O ₃ (8) + Ta ₂ O ₃ (0.5) 115 1000 18 Y ₂ O ₃ (8) + Li ₂ O (0.5) 90 900 19 Y ₂ O ₃ (8) + CaO (0.5 ) 95 880 20 Y ₂ O ₃ (4) + Sm ₂ O ₃ (4) + MgO (0.3) + Ta ₂ O ₃ (0.2) 100 1000 21 * Y ₂ O ₃ (0.4) + MgO (1) 80 680 22 * Y ₂ O ₃ (15) + MgO (0.5) 75 850 23 * Sm ₂ O ₃ (0.4) + TiO ₂ (5) 70 500 24 * Sm ₂ O ₃ (15) 75 830 25 * Yb ₂ O ₃ (0.4) + CaO (1.0 ) 65 600 26 * Yb ₂ O ₃ (15) 65 800 (Note) Samples marked with * in the table are comparative examples.

As can be seen from the results, the rare earth oxide added as a sintering aid has a thermal conductivity of 100 W / m · even when Yb ₂ O ₃ or Sm ₂ O ₃ is used in addition to Y ₂ O _3. A Si ₃ N ₄ substrate having excellent characteristics of not less than K and a three-point bending strength of not less than 900 MPa can be obtained. In particular, in the case of sample 12 using Yb ₂ O ₃ , a substrate having an extremely high thermal conductivity of 140 W / m · K can be obtained. Was done. In Samples 16 to 20, Ti, Ta, L other than MgO were used as sintering aids other than rare earth oxides.
1% by weight or less of each oxide of i and Ca was added. Even when these oxides are used, 1800 ° C.
A dense Si ₃ N ₄ sintered body could be obtained by sintering at the following low temperature.

On the other hand, in Samples 21 to 26, which are comparative examples, in which the amount of the rare earth oxide added was as small as 0.4% by weight, the amount of liquid phase generated in the process of densification of Si ₃ N ₄ particles was small. However, despite sintering at a high temperature of 1950 ° C., a dense sintered body could not be obtained. As a result, the thermal conductivity of the obtained Si ₃ N ₄ sintered body was low, and the value of the three-point bending strength was also low. Conversely, when the added amount of the rare earth oxide was as large as 15% by weight, the volume ratio occupied by the grain boundary phase with respect to the entire sintered body was increased, so that the thermal conductivity was lowered.

Next, each of the above Si ₃ N ₄ sintered bodies was processed into a Si ₃ N ₄ substrate having a thickness of 2 mm in the same manner as in Example 1, and the amount of warpage per 25.4 mm of the substrate length was measured. ,
An oxygen-free copper plate having a thickness of 0.3 mm was joined to the concave main surface using a brazing material containing an active metal. For each of the obtained ceramic composite substrates, as in Example 1, the presence or absence of cracks and the number of heat cycles up to the occurrence of cracks were confirmed by a heat cycle test, and the thermal resistance was measured to examine the heat dissipation characteristics of the entire circuit. Was. The results are shown in Table 3 below.

[0037]

[Table 3] (Note) Samples marked with * in the table are comparative examples.

As described above, in each of the samples 11 to 20 of the present invention in which the Si ₃ N ₄ substrate excellent in thermal conductivity and mechanical strength is used and the thickness of the substrate and the thickness of the copper plate are at a predetermined ratio, A ceramic composite substrate having excellent characteristics and heat radiation characteristics was obtained. However, in Samples 21 to 26 of the comparative example, Si ₃
Since the thermal conductivity of the N ₄ substrate is low, the thermal resistance of the composite substrate is high, and in particular, Sample 2 using a Si ₃ N ₄ substrate, which is inferior in strength.
It can be seen that cracks easily occur in the substrates 1, 23, and 25 due to thermal shock in the heat cycle test.

[0039]Example 3  As shown in Table 4 below, in samples 27 to 32,
By changing the amount of oxygen or Al_ThreeN_FourManufactured sintered body
Other than the above, Si_ThreeN_FourMake a substrate, and
The thermal conductivity and the three-point bending strength were similarly evaluated. these
The results are shown in Table 4. Also implemented for reference
Si of Example 1_ThreeN_FourThe substrate (sample 1) is also shown.
Was.

[0040]

[Table 4] Impurities in raw material powder Thermal conductivity 3-point bending strength Sample sintering aid (wt%) Oxygen (wt%) Al (wt%) (W / m · K) (MPa) 1 Y ₂ O ₃ (8) + MgO (0.5) 1 0.1 110 950 27 Y ₂ O ₃ (8) + MgO (0.5) 2 0.1 95 1100 28 Y ₂ O ₃ (8) + MgO (0.5) 0.5 0.1 120 930 29 Y ₂ O ₃ (8 ) + MgO (0.5) 1 0.2 90 1200 30 Y ₂ O ₃ (8) + MgO (0.5) 1 0.05 120 900 31 * Y ₂ O ₃ (8) + MgO (0.5) 3 0.1 70 1200 32 * Y ₂ O ₃ (8 ) + MgO (0.5) 1 0.5 50 1250 (Note) Samples marked with * in the table are comparative examples.

As the amount of oxygen or Al in the raw material powder increases, the sinterability of Si ₃ N ₄ improves, so that the resulting sintered body becomes dense and the mechanical strength improves. However, on the other hand, the thermal conductivity of the Si ₃ N ₄ sintered body decreased. This is because the solid solution of oxygen and Al in the Si ₃ N ₄ grains makes the original crystal structure of the Si ₃ N ₄ crystal more complicated, and phonons are significantly scattered in the grains.

Next, each of Samples 27 to 32 in Table 4
_{As for the 3} N ₄ sintered body, the S
The substrate was processed into an i ₃ N ₄ substrate, the amount of warpage per substrate length of 25.4 mm was measured, and the thickness of the concave main surface was 0.3 m.
m oxygen-free copper plates were joined using a brazing material containing an active metal. Example 1 about each obtained ceramic composite substrate
Similarly to the above, the presence / absence of crack generation and the number of heat cycles until crack generation were confirmed by a heat cycle test, and the heat resistance was measured to examine the heat radiation characteristics of the entire circuit. The results are shown in Table 5 below.

Further, using the Si ₃ N ₄ substrate of Sample 1 shown in Table 4 above, the substrate was processed into a Si ₃ N ₄ substrate having a thickness of 2 mm.
As a, an aluminum plate having a thickness of 0.3 mm was joined to the concave main surface by a brazing material containing aluminum.
Further, as Sample 1-b, aluminum plates each having a thickness of 0.3 mm were joined to both main surfaces of the Si ₃ N ₄ substrate of Example 1 in the same manner as described above. Each of the obtained composite substrates was evaluated by the same method as described above, and the results are shown in Table 5.

[0044]

[Table 5] tc / tm warpage cracking during thermal resistance specimen metal layer (tc / ttm) (μm / in) the number of crack heat cycle number (℃ / W) 27 Cu 6.7 80 0> 3000 0.7 28 Cu 6.7 100 0> 3000 0.5 29 Cu 6.7 80 0> 3000 0.65 30 Cu 6.7 90 0> 3000 0.45 31 * Cu 6.7 110 0> 3000 1.8 32 * Cu 6.7 105 0> 3000 1.9 1−a Al 6.7 100 0> 3000 1.0 1− b Al (both sides) 3.3 100 0> 3000 0.7 (Note) Samples marked with * in the table are comparative examples.

As can be seen from the above results, each of the samples 27 to 30 of the present invention using a Si ₃ N ₄ substrate excellent in thermal conductivity and mechanical strength and having a predetermined ratio of the thickness of the substrate to the thickness of the copper plate. In samples 1-a to 1-b, ceramic composite substrates having excellent heat cycle characteristics and heat radiation characteristics were obtained. However, in the samples 31 to 32 of the comparative examples, the thermal resistance of the composite substrate was extremely high because the thermal conductivity of the Si ₃ N ₄ substrate was low.

As can be seen from the results of Samples 1-a and 1-b, even if an aluminum plate was used as the metal plate to be bonded to the Si ₃ N ₄ substrate instead of the copper plate, a composite substrate having good heat radiation characteristics was obtained. was gotten.

[0047]

According to the present invention has a high thermal conductivity than conventional the Si ₃ N ₄ sintered body, also using the Si ₃ N ₄ substrate having both the mechanical strength at the same time, and Si ₃ N ₄ By adjusting the thickness of the board and the thickness of the metal layer bonded to the board to a specific range, it can withstand the mechanical load at the time of mounting or mounting,
Further, a ceramic composite substrate having excellent heat cycle characteristics and heat radiation characteristics can be provided.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Masaji Yoshimura 1-1-1 Kunyokita, Itami City, Hyogo Prefecture F-term in Sumitomo Electric Industries, Ltd. Itami Works 4G026 BA17 BB23 BB27 BC01 BD14 BF11 BH07 5E338 AA01 AA02 AA18 CC01 CD11 EE02

Claims (8)

[Claims] 1. A silicon nitride ceramic comprising: a silicon nitride ceramic substrate having a thermal conductivity of 90 W / m · K or more and a three-point bending strength of 700 MPa or more; and a metal layer bonded on one main surface thereof. When the thickness of the substrate is tc and the thickness of the metal layer is tm, the relational expression 2tm ≦ t
A silicon nitride composite substrate, wherein c ≦ 20 tm is satisfied. 2. A silicon nitride ceramic comprising: a silicon nitride ceramic substrate having a thermal conductivity of at least 90 W / m · K and a three-point bending strength of at least 700 MPa; and a metal layer bonded on both main surfaces thereof. Assuming that the thickness of the substrate is tc and the total thickness of the metal layers on both main surfaces is ttm, tc and ttm
Satisfies the relational expression ttm ≦ tc ≦ 10ttm. 3. The silicon nitride composite substrate according to claim 1, wherein the silicon nitride ceramic substrate before the metal plate bonding has a warp such that a main surface on a side on which the semiconductor element is mounted is concave. . 4. The method according to claim 3, wherein the amount of the warpage is 10 to 300 μm per 25.4 mm of the substrate length.
3. The silicon nitride composite substrate according to 1.). 5. The silicon nitride ceramic substrate according to claim 1, wherein said rare earth element is converted to an oxide in an amount of 0.6 to 10% by weight,
g, at least one element selected from the group consisting of Ti, Ta, Li, and Ca in an amount of 0.5 to 1.0% by weight in terms of oxides, oxygen as an impurity of 2% by weight or less, and Al The silicon nitride composite substrate according to any one of claims 1 to 4, wherein the silicon nitride composite substrate contains 0.2% by weight or less in terms of oxide. 6. The silicon nitride composite substrate according to claim 5, wherein said rare earth element is at least one selected from Y, Sm and Yb. 7. The silicon nitride composite substrate according to claim 1, wherein said metal layer is made of a metal containing copper as a main component. 8. The silicon nitride composite substrate according to claim 1, wherein said metal layer is made of a metal containing aluminum as a main component.